It has previously been proposed to monitor tire pressure by a transducer within each vehicle tire. Several schemes have been tried for advising the vehicle operator of tire pressure conditions, especially in the case of low tire pressure. It is known, for example, to generate a visible signal at the tire and to visually inspect the signal. It is also known to generate a magnetic field at the transducer in response to a low pressure condition, to detect the field by a detector mounted near each wheel, and to display a warning on the instrument panel. It has also been proposed to mount a transducer and radio transmitter within each tire and a receiver on the vehicle dedicated to processing transmitted tire pressure data and displaying necessary information.
For the radio transmission type of pressure data communication it is desirable that rather than requiring a dedicated stand-alone receiver and processor unit, that this function be coordinated with another vehicle function to reduce system expense as well as power drain on the vehicle battery.
Regarding the transmitter side of a radio transmission system, the energy for supplying the transmitter may be generated by tire rotation, in which case information on a low tire pressure condition occurring when the vehicle is not in use cannot be displayed until after vehicle movement begins. Alternatively, the energy may be supplied by a battery, but then considerations of battery life come into play. It is desirable that battery life be very long, perhaps as long as vehicle life, while not compromising the amount or frequency of tire condition information delivered by the system. It is desirable to know, in addition to low pressure condition, when correct pressure is restored, which tire is affected, and the operability of the transmitter units.